Fluid motor control mechanism

ABSTRACT

A normally closed pilot controllable exhaust valve mechanism governs the discharge of return fluid from the exhaust passage of a fluid motor control mechanism. A first pilot instrumentality effects opening of the exhaust valve mechanism in consequence of rise in pressure of fluid in the exhaust passage to a predetermined value. A second pilot instrumentality effects opening of the exhaust valve mechanism at times when the pressure of fluid in a source connected supply fluid passage rises to a predetermined value exceeding the first, to assure that there will be substantially no obstruction to discharge of exhaust fluid from the exhaust passage at times when a hydraulic motor governed by the control mechanism is under heavy load.

United States Patent Primary Examiner-Laveme D. Geiger Assistant Examiner-David J Zobkiw Att0mey1ra Milton Jones ABSTRACT: A normally closed pilot controllable exhaust valve mechanism governs the discharge of return fluid from the exhaust passage of a fluid motor control mechanism. A first pilot instrumentality effects opening of the exhaust valve mechanism in consequence of rise in pressure of fluid in the exhaust passage to a predetermined value. A second pilot instrumentality effects opening of the exhaust valve mechanism at times when the pressure of fluid in a source connected supply fluid passage rises to a predetermined value exceeding the first, to assure that there will be substantially no obstruction to discharge of exhaust fluid from the exhaust passage at times when a hydraulic motor governed by the control mechanism is under heavy load.

| y 50 48 40 k v I l nh- Iv 1 l l l I 49 5/ 43 I 3a. 46 1 l 39 l l l l l 1 1 39 {O\\} 157 5t, 2t, 41 v 27 37 38 FLUID MOTOR CONTROL MECHANISM This invention relates to fluid motor controls, and has more particular reference to valve mechanisms such as are used for the control of reversible fluid motors, including double-acting hydraulic cylinders.

The main purpose of the invention resides in the provision of a fluid motor control mechanism having high-pressure fluid supply and low-pressure fluid return passages, and which features means for effecting elevation to and maintenance of the pressure of motor exhaust fluid in the low-pressure fluid return passage at a predetermined positive value as long as the pressure of fluid in the fluid supply passage is below a predetermined value.

More specifically, it is an object of the invention to provide in a fluid motor control device a fluid pressure actuatable exhaust valve mechanism which is maintained either fully closed or fully open, depending upon the pressure value of fluid in a supply passage of the control device.

From this it will be seen that it is a purpose of the invention to provide a fluid motor control device with an exhaust valve mechanism which will not be subject to objectionable hunting between partially open and closed positions.

Still another object of the invention resides in the provision of a fluid motor control device such as described above, which is exceptionally well suited for the prevention of voids in a hydraulic cylinder governed by said device.

With these observations and objectives in mind, the manner in which the invention achieves its purpose will be appreciated from the following description and the accompanying drawing, which exemplifies the invention, it being understood that such changes in the specific apparatus disclosed herein may be made as come within the scope of the appended claims.

The accompanying drawing illustrates one complete example of the embodiment of the invention constructed according to the best mode so far devised for the practical application of the principles thereof, and in which the single FlGURE diagrammatically illustrates a hydraulic control valve mechanism embodying this invention.

As therein shown by way of example, the control valve mechanism comprises two sections of a sectional valve mechanism, namely, a motor control section 5, and an outlet section 6 to which the control section is secured with pressure fluid supply and return passages 7 and 8, respectively in each section in register with one another and providing supply and return headers 7 and 8' respectively.

The control section contains an elongated valve spool 10 which is axially slidable in a bore 11 in the body of the control section between a neutral position (shown) and a pair of operating positions at opposite sides of neutral. The spool is operable to communicate either of a pair of service ports 12 and 13 with the fluid supply passage 7 while at the same time communicating the other service port with the return passage 8 via an exhaust passage 14 in the body of the control section.

The control section is adapted to govern the operation of a reversible fluid motor, such as a double-acting cylinder 15, in that it enables pressure fluid from a pump P to be directed into either end of the cylinder while at the same time providing for exhaust of fluid from the other end of the cylinder to a reservoir via the exhaust passage 14 and return header 8'.

Though the supply passage 7 is at all times communicated with the outlet of the pump, the latter is unloaded in a neutral position of the valve spool shown through an open center passage in the control section. The open center passage can be of the type illustrated by way of example as comprising a pair of upstream branches l6 spaced from but flanking a single downstream branch 17. The downstream branch can be communicated substantially directly with the reservoir in any adjacent upstream branch 16 of the open center passage. The supply passage 7 is communicated with the high-pressure bridge passage 18 through the customary check valve 217 The exhaust passage 14 can be considered as a low-pressure bridge passage having a pair of branches 22 and 23, one for each service passage l2'-l3. These branches open to the bore 11 at zones axially outwardly of their respective service passages.

As is customary in control valves of the type described, movement of the valve spool 10 to its operating position to the right of neutral closes off the open center passage and diverts pressure fluid to supply passage 7 and to the service port 12 via the left-hand branch 19 of the high-pressure bridge 18, and a groove in the adjacent portion of the valve spool, and the service passage 12'. At the same time, the service port 13 is communicated with the return passage 8 via service passage 13, a groove in the adjacent portion of the valve spool, and the right-hand branch 23 of the low-pressure bridge passage 14. These connections of the service ports'with the supply and exhaust passages are reversed when the valve spool is moved to its operating position to the left of neutral.

ln each of said operating positions of the valve spool 10, fluid exhausted from the cylinder 15 enters the return passage 8 and flows through the return header 8' to an exhaust chamber 25 in the outlet section 6 of the control valve mechanism. Such exhaust fluid must flow into an outlet passage 26 for return to the reservoir.

An exhaust valve mechanism 27, however, governs such discharge flow of exhaust fluid from the exhaust chamber 25. The exhaust valve mechanism comprises a fluid-pressure responsive plunger 28 which is urged by a spring 29 axially toward engagement with an annular seat 30, through which seat the exhaust chamber 25 is communicated with the outlet passage 26. The plunger 28 is hollow, and it has a small hole 32 in its seat engaging end to allow exhaust fluid in the chamber 25 to flow into the hollow interior of the plunger to a pressure chamber 33 behind it. Consequently, the spring 29 as well as pressure fluid in the pressure chamber 33 exerts closing force on the plunger 28 of the exhaust valve mechanism to hold it closed.

The plunger 28, of course, is adapted to be opened under force exerted on its seat engaging end by the pressure of return fluid in the exhaust chamber 25. It will not respond to such spending force, however, until the pressure chamber 33 behind it is vented to allow fluid therein to flow through an outlet 34 to the outlet passage 26.

According to this invention, the outlet 34 of pressure chamber 33 is communicable with the outlet passage 26 through either of a pair of venting passages governed by fluidpressure-responsive pilot valve mechanisms 35 and 36, which are respectively responsive to the pressure of fluid in the exhaust chamber 25 and in the supply passage 7 and its header 7 One of these venting passages 37 has an annular valve seat 38 formed therein, and the other venting passage 39 similarly has an annular valve seat 40 formed in it. A pilot poppet 41 is urged by a spring 42 into engagement with the seat 38, and another pilot poppet 43 is urged by a spring 44 into engagement with its seat 40. The spring forces with which the pilot poppets 41 and 42 are held on their seats can be varied by means of adjusting screws 45 and 46 respectively.

As can be readily seen, the pressure of return fluid in the chamber 33 for the exhaust valve plunger 28 at all times exerts opening force upon the pilot poppet 41. Similarly, the pressure of supply fluid in passage 7 and its header 7' is utilized to exert opening force on the pilot poppet 43. For this latter purpose, the pilot poppet 43 is provided with a plunger or stem 48 which extends into a passage 49 that can be communicated with the supply passage portion 7 in the outlet section, or in any suitable way with the supply header 7'. The stem 48 not only serves to guide the seating and unseating motions of the pilot poppet 43, but it also carries a seal 50 to prevent leakage of supply fluid from the header 7' into an annular chamber 51 surrounding the stem and located downstream from the poppet seat 40, between the latter and the seal 50. The downstream branch of the venting passage 39 governed by the pilot poppet 43 communicates the chamber 51 with the outlet passage 26.

The pilot poppet 41 is adapted to be opened when the pressure of exhaust fluid in communicated chambers 25 and 33 reaches a predetermined value; while the pilot poppet 43 is adapted to be opened when the pressure of fluid in the supply header 7' reaches a higher predetermined value. Merely by way of example, the spring 42 for the pilot poppet 41 can be set to allow the latter to open whenever the pressure of fluid in the exhaust chamber 25 rises to a value of 300 p.s.i.; and the spring 44 for pilot poppet 43 can be set to allow the same to open when pressure of fluid in the supply header 7' reaches a value of 1,000 p.s.i.

As will be appreciated from the description thus far, the exhaust valve mechanism constitutes an obstruction to and precludes free discharge of fluid from the exhaust chamber 25 except at such times as the pressure of exhaust fluid in said chamber exceeds 300 p.s.i., or when the pressure of supply fluid in header 7 exceeds 1,000 p.s.i. The pressure of fluid in the supply header, of course, is determined by the load on the cylinder governed by the control valve mechanism 5.

If the load on the cylinder is substantial, the pressure of fluid in the supply header 7 can easily exceed the I,000 p.s.i. setting for pilot poppet 43, and the latter will be held open to vent the pressure chamber 33 for the plunger 28 of the exhaust valve mechanism, thereby allowing the latter to be held open by the force of return fluid in the exhaust chamber 25. At such times, therefore, there will be no objectionable obstruction to the flow of return fluid from the cylinder 15 to the reservoir.

There are times, however, when the nature of the load operated by the cylinder causes expulsion of fluid from one end thereof faster than the pump can supply fluid to the other end of the cylinder. When this occurs, an objectionable void is created in the expanding end of the cylinder.

Various anticavitation or void control schemes have been proposed in the past to overcome this objection. The most successful of them relied upon cylinder port relief and check valve combinations and passages by which load-pressurized fluid from the contracting end of the cylinder could flow back to its expanding end, together with fluid from the pump. Such cylinder port relief and check valve combinations are diagrammatically illustrated as embodied in the control section 5. As therein seen, each exhaust passage branch 22-23 extends alongside its associated service passage l2'13 and is communicated therewith through a cylinder port relief valve 53 and also through a check valve 54. The relief valve 53 associated with either service port will open when the pressure of exhaust fluid in said port achieves a predetermined relief value, to allow such fluid to flow around the low-pressure bridge passage 14 and to pass through the check valve 54 associated with the other service passage, for recirculation to the expanding end of thecylinder and the relief of a void therein.

The exhaust valve mechanism 27 is a valuable adjunct to the above-described void control scheme. In effect, it closes off the low-pressure bridge passage 14 from the reservoir until a predetermined pressure obtains in the exhaust chamber 25, thus assuring that load-pressurized fluid from the contracting end of the cylinder will be available for recirculation back to the expanding end of the cylinder at pressure values that can exceed the 300 p.s.i. mentioned hereinbefore, depending upon the adjustment of the screw 45 bearing upon the spring 42 of the pilot poppet 41.

It is a feature of this invention that void prevention can be achieved without reliance upon the above-mentioned cylinder port relief and check valve combinations. For this purpose, the exhaust chamber in the outlet section 6 can be communicated with the supply passage 7 and header 7' by means ofa passageway 56 having a check valve 57 therein. Consequently,

exhaust fluid from the chamber 25 can flow through the check valve controlled passageway 56 and the supply header 7 to the supply passage 7 in the control section 5 whenever the pressure of supply fluid in the header 7 drops to a value below the pressure of fluid in the exhaust chamber 25. The exhaust fluid thus flowing to the supply passage 7 in the control section 5 can then flow past the check valve 21 to the supply bridge 18 and to whichever cylinder port is in communication therewith. In this way, exhaust fluid recirculated back to the supply passage 7 in the control section 5 will augment the flow of pump output fluid to the expanding end of the cylinder to prevent formation of a void therein. It should again be observed, of course, that the exhaust fluid thus led back to the control section 5 will be load-pressurized fluid maintained under substantial pressure, because of the obstruction which the exhaust valve mechanism 27 presents to free flow of ex haust fluid to the reservoir.

If desired, the last-described antivoid means can be used with the highpressure relief and check valve combinations described earlier, which function for void relief at times when the valve spool is returned to its neutral position also.

As stated before, however, it is undesirable to restrict exhaust flow to the reservoir at times when the hydraulic cylinder is heavily loaded. The pressure conditions in the supply header 7' are then the reverse of what they are when the cylinder is driven by the load, since the pressure in the supply header increases in proportion to the load on the cylinder. It is for this reason that the obstruction to exhaust flow provided by the exhaust valve mechanism 27 is displaced at times when the cylinder. is heavily loaded. Then, the exhaust valve mechanism is caused to open under the force of exhaust fluid acting on its seat engaging end, as soon as the pressure of fluid in the supply header reaches a predetermined value, such as the 1,000 p.s.i. mentioned before or even a higher value, depending upon the setting of the spring-adjusting screw for the pilot poppet 43.

It is also important to observe that the exhaust valve mechanism 27 is either fully open, or fully closed. When it is closed, the force of its spring 29 is augmented by the closing force which exhaust fluid in the chamber 33 exerts upon the rear of the plunger 28. It opens whenever its chamber 33 is vented through either of the pilot valve mechanisms 35 or 36, in response to the force which exhaust fluid in the chamber 25 exerts upon the seat-engaging end of plunger 28. The plunger 28 is never partly open during operation of the cylinder 15 under the control of the valve spool 10. It can only be fully open or fully closed, depending upon the conditions of the two pilot poppets that govern it.

From the foregoing description, together with the accompanying drawing, it will be readily apparent to those skilled in the art that this invention provides a significant advance in the art relating to control valve mechanisms with void control.

lclaim:

1. In combination with a fluid motor control mechanism having a first passage connectable with a fluid pressure source, and a second passage through which motor exhaust fluid can be returned to a reservoir:

A. a pilot controllable exhaust valve mechanism to normally block discharge flow of exhaust fluid from said second passage;

B. and pilot control means for said exhaust valve mechanism, comprising 1. a first pilot instrumentality which is operable to effect opening of the exhaust valve mechanism whenever the pressure of exhaust fluid in said second passage rises to a first predetermined value,

2. and a second pilot instrumentality which is operable to effect opening of the exhaust valve mechanism in consequence of rise in the pressure of source fluid in said first passage to a predetermined value in excess of said first predetermined value.

2. The combination of claim I, further characterized by:

A. means providing a passageway communicating said first and second passages;

B. and a nonreturn valve in said passageway, providing for flow of exhaust fluid from said second passage to the first passage whenever pressure of source fluid in the latter drops to a value below that of exhaust fluid in said second passage.

3. The combination of claim 1, further characterized by:

A. said exhaust valve mechanism being I. fluid pressure responsive,

2. normally held closed by the pressure of fluid in a chamber with which the exhaust valve mechanism is associated and which is communicated with the exhaust passage to receive exhaust fluid therefrom,

3. and movable to open position in response to force exerted thereon by pressure of fluid in the exhaust passage at times when said chamber is vented;

B. and said pilot control means controlling venting of said chamber.

4. The combination of claim 1, further characterized by:

A. said exhaust valve mechanism being l. pressure responsive,

2. normally held closed by the pressure of exhaust fluid manifested in a chamber with which the exhaust valve mechanism is associated,

3. and movable to open position in response to force exerted thereon by pressure of fluid in the exhaust passage at times when said chamber vented;

B. and said pilot control means comprising first and second vent passageways leading from said chamber,

1. said pilot instrumentalities comprising a pair of pilot valves, one for each vent passageway.

5. In combination with a fluid motor control mechanism having a high-pressure passage connectable with a fluid pressure source, and a low-pressure passage through which motor exhaust fluid can be returned to a reservoir:

A. a pilot controllable exhaust valve mechanism normally blocking discharge of exhaust fluid from the low-pressure passage, said exhaust valve mechanism comprising i. a pressure chamber which is communicated with the low-pressure passage,

2. and a pressure-actuated valve member in said chamber, adapted to be held closed by pressure of exhaust fluid in the chamber, and adapted to be opened by pressure of exhaust fluid in the low-pressure passage at times when the chamber is vented;

B. means defining first and second passageways through which said chamber can be vented;

C. pilot means normally closing said first passageway and movable to open position in consequence of increase in pressure of fluid in the low-pressure passage to a first predetermined value;

D. and other pilot means normally closing said second passageway and movable to open position in consequence of increase in pressure of fluid in the high-pressure passage to a predetermined value in excess of said first predetermined value.

6. A fluid motor control instrumentality having an outlet passage and a pressure fluid supply passage from which the ports of a reversible hydraulic motor can receive working fluid, characterized by:

A. an exhaust passage which leads to said outlet passage;

B. a check-valve-controlled bypass through which fluid in the exhaust passage can flow to the supply passage;

C. a pilot controllable valve member normally blocking exhaust fluid flow to the outlet passage but movable to open position under force exerted thereon by pressure of fluid in the exhaust passage provided pressure fluid can escape from a chamber in which a portion of the valve member operates;

D. and first and second pilot mechanisms each operable to effect venting of said chamber so that the valve member can open in consequence of force exerted thereon by pressure fluid in the exhaust passage,

1. said first pilot mechanism being operable in response to rise in pressure in the exhaust passage to a predetermined value, 2. and said second pilot mechanism being operable in response to rise in pressure in the supply passage to a predetermined value in excess of said first designated pressure value.

7. A fluid motor control mechanism of the type having a movable valve element for selectively directing pressure fluid from a supply passage to either of a pair of service passages while concurrently directing to an exhaust passage pressure fluid returning to the nonselected service passage, characterized by:

A. a check valve controlled antivoid passage through which fluid can flow to one of said service passages form the exhaust passage;

B. a pilot controllable exhaust valve mechanism to normally block discharge of fluid from the exhaust passage;

C. a first pilot instrumentality for the exhaust valve mechanism operable to effect opening thereof in consequence of pressure of fluid in the exhaust passage only after said exhaust fluid pressure has increased to a predetermined value, whereby pressurized exhaust fluid will be available for flow along a first path leading through the exhaust passage and said antivoid passage to said one service passage at times when the pressure of supply fluid being directed thereto by the valve element drops to a value below that of fluid in the exhaust passage at said increased pressure;

D. a check-valve-controlled bypass communicating the exhaust passage with the supply passage to provide for flow of pressurized exhaust fluid to said one service passage, at said aforementioned times, along a second path which leads through the supply passage;

E. and a second pilot instrumentality which is operable to effect opening of the exhaust valve mechanism as a consequence of rise in pressure in the supply passage to a second predetermined value above said first-mentioned predetermined value, so as to provide for substantially unrestricted discharge of exhaust fluid from either nonselected service passage at times when the pressure of supply fluid directed to the selected service passage rises to said second predetermined value. 

1. In combination with a fluid motor control mechanism having a first passage connectable with a fluid pressure source, and a second passage through which motor exhaust fluid can be returned to a reservoir: A. a pilot controllable exhaust valve mechanism to normally block discharge flow of exhaust fluid from said second passage; B. and pilot control means for said exhaust valve mechanism, comprising
 1. a first pilot instrumentality which is operable to effect opening of the exhaust valve mechanism whenever the pressure of exhaust fluid in said second passage rises to a first predetermined value,
 2. and a second pilot instrumentality which is operable to effect opening of the exhaust valve mechanism in consequence of rise in the pressure of source fluid in said first passage to a predetermined value in excess of said first predetermined value.
 2. and a second pilot instrumentality which is operable to effect opening of the exhaust valve mechanism in consequence of rise in the pressure of source fluid in said first passage to a predetermined value in excess of said first predetermined value.
 2. The combination of claim 1, further characterized by: A. means providing a passageway communicating said first and second passages; B. and a nonreturn valve in said passageway, providing for flow of exhaust fluid from said second passage to the first passage whenever pressure of source fluid in the latter drops to a value below that of exhaust fluid in said second passage.
 2. normally held closed by the pressure of fluid in a chamber with which the exhaust valve mechanism is associated and which is communicated with the exhaust passage to receive exhaust fluid therefrom,
 2. normally held closed by the pressure of exhaust fluid manifested in a chamber with which the exhaust valve mechanism is associated,
 2. and a pressure-actuated valve member in said chamber, adapted to be held closed by pressure of exhaust fluid in the chamber, and adapted to be opened by pressure of exhaust fluid in the low-pressure passage at times when the chamber is vented; B. means defining first and second passageways through which said chamber can be vented; C. pilot means normally closing said first passageway and movable to open position in consequence of increase in pressure of fluid in the low-pressure passage to a first predetermined value; D. and other pilot means normally closing said second passageway and movable to open position in consequence of increase in pressure of fluid in the high-pressure passage to a predetermined value in excess of said first predetermined value.
 2. and said second pilot mechanism being operable in response to rise in pressure in the supply passage to a predetermined value in excess of said first designated pressure value.
 3. and movable to open position in response to force exerted thereon by pressure of fluid in the exhaust passage at times when said chamber vented; B. and said pilot control means comprising first and second vent passageways leading from said chamber,
 3. and movable to open position in response to force exerted thereon by pressure of fluid in the exhaust passage at times when said chamber is vented; B. and said pilot control means controlling venting of said chamber.
 3. The combination of claim 1, further characterized by: A. said exhaust valve mechanism being
 4. The combination of claim 1, further characterized by: A. said exhaust valve mechanism being
 5. In combination with a fluid motor control mechanism having a high-pressure passage connectable with a fluid pressure source, and a low-pressure passage through whicH motor exhaust fluid can be returned to a reservoir: A. a pilot controllable exhaust valve mechanism normally blocking discharge of exhaust fluid from the low-pressure passage, said exhaust valve mechanism comprising
 6. A fluid motor control instrumentality having an outlet passage and a pressure fluid supply passage from which the ports of a reversible hydraulic motor can receive working fluid, characterized by: A. an exhaust passage which leads to said outlet passage; B. a check-valve-controlled bypass through which fluid in the exhaust passage can flow to the supply passage; C. a pilot controllable valve member normally blocking exhaust fluid flow to the outlet passage but movable to open position under force exerted thereon by pressure of fluid in the exhaust passage provided pressure fluid can escape from a chamber in which a portion of the valve member operates; D. and first and second pilot mechanisms each operable to effect venting of said chamber so that the valve member can open in consequence of force exerted thereon by pressure fluid in the exhaust passage,
 7. A fluid motor control mechanism of the type having a movable valve element for selectively directing pressure fluid from a supply passage to either of a pair of service passages while concurrently directing to an exhaust passage pressure fluid returning to the nonselected service passage, characterized by: A. a check valve controlled antivoid passage through which fluid can flow to one of said service passages form the exhaust passage; B. a pilot controllable exhaust valve mechanism to normally block discharge of fluid from the exhaust passage; C. a first pilot instrumentality for the exhaust valve mechanism operable to effect opening thereof in consequence of pressure of fluid in the exhaust passage only after said exhaust fluid pressure has increased to a predetermined value, whereby pressurized exhaust fluid will be available for flow along a first path leading through the exhaust passage and said antivoid passage to said one service passage at times when the pressure of supply fluid being directed thereto by the valve element drops to a value below that of fluid in the exhaust passage at said increased pressure; D. a check-valve-controlled bypass communicating the exhaust passage with the supply passage to provide for flow of pressurized exhaust fluid to said one service passage, at said aforementioned times, along a second path which leads through the supply passage; E. and a second pilot instrumentality which is operable to effect opening of the exhaust valve mechanism as a consequence of rise in pressure in the supply passage to a second predetermined value above said first-mentioned predetermined value, so as to provide for substantially unrestricted discharge of exhaust fluid from either nonselected service passage at times when the pressure of supply fluid directed to the selected service passage rises to said second predetermined value. 